One of the problems facing the carpet industry is the production of a carpet underlayment pad which will hold the carpet in place and provide wear protection as well as a good cushion for the carpet. In order to prevent slippage between the carpet and the pad and between the pad and the surface on which it rests, adhesive coatings have traditionally been applied directly to the surface of carpets or underlayment pads. Typically, the carpet or pad is suspended on a tenter frame for application of the adhesive in the form of a frothed emulsion. The suspended carpet or pad is then passed through an oven to dry the adhesive coating. This method of application has several disadvantages. For example, liquid emulsion is absorbed into the inner layers of the porous surface before the adhesive dries which stiffens the carpet or pad and hinders its performance. The drying step can damage the synthetic fibers of the pad, especially if the pad contains heat sensitive synthetic fibers such as polypropylene, because drying is usually conducted at high temperatures in order to attain reasonable production speeds with ovens of reasonable length. In addition, the adhesive layer is often uneven because of the uneven surface of the carpet or pad and results in variable adhesive strength and wasted adhesive.
Examples of systems which have been devised to overcome the problems associated with direct application of adhesives to the surface of carpets and underlayment pads are described below.
German patent document 7124118.4 discloses covering at least one side of a carpet underlay, made of an elastic material such as polyvinyl chloride or foamed latex, with an adhesive glue based on dispersion. The adhesive glue is covered with a transparent foil which must be pulled off before use of the underlay.
U.S. Pat. No. 4,557,774 and U.S. Pat. No. 4,797,170 disclose installation of wall-to-wall carpet and pad without the need for stretching and tacking by using a pad with pressure-sensitive adhesive on one or both surfaces. To keep the adhesive at the surface of the foam pad, a sealant is applied to the pad before the pressure sensitive adhesive is applied or the pad is heat treated to form a stiffened surface or crust before application of the adhesive.
CA 2,032,083 discloses use of a hot melt pressure sensitive adhesive on the porous surface of carpet pads. It also discloses use of a pressure sensitive adhesive on the surface of a carpet pad which has first been treated with a film or sealant.
U.S. Pat. No. 5,160,770 discloses a carpet pad which has pressure sensitive adhesive preapplied on one or both surfaces for retaining the pad and carpet in place on the floor by adhesion without the need for stretching. When a water-based pressure sensitive adhesive is used, a coating or sealant is applied to the surface of the carpet pad before the pressure sensitive adhesive is applied in order to prevent wicking-in of the adhesive. The padding surface does not need to be coated when a hot melt adhesive is used.
U.S. Pat. No. 5,221,394 discloses a process for making backed, pressure-adherent carpeting wherein an adhesive is deposited as a layer on a supporting liner. The adhesive is then applied to one side of a backing film, and then, in a separate step, the other side of the backing film is heat-laminated to a web of carpeting to thereby reinforce the carpeting and provide it with an adhesive. The carpeting is both reinforced and rendered adherent in a single pass of the carpeting and at a single station in the carpet-manufacturing line.